Cross-structures in the lachlan Orogen: the Lachlan Transverse Zone example

The Lachlan Transverse Zone is a major yet subtle west-northwest-trending s tructure that cuts across the Tasmanides of southeastern Australia. It exte nds from the western part of the Olepoloko Fault in the west, where it mark s the boundary between the Delamerian and Thomson Orogens, across the Lachl an Orogen into the Sydney Basin where it is represented by dykes and intrus ions. The western part of the Lachlan Transverse Zone is defined by west-no rthwest-trending faults. In the Eastern Belt of the Lachlan Orogen, it is d efined as a corridor of west-northwest-trending folds and faults that disru pt major folds and faults which constitute the regional grain of the orogen . The Lachlan Transverse Zone was active in the development of the Lachlan Orogen since at least the Middle Ordovician period. It has influenced the p artitioning of upper crustal extensional and contractional deformation, the intrusion of igneous bodies as well as the distribution of copper-gold dep osits in the Eastern Belt of the orogen. The Lachlan Transverse Zone appear s to be an extension of the Proterozoic Amadeus Transverse Zone, as well as an extension of a west-northwest-trending transform segment in the Tasman Line that controlled the Neoproterozoic and Cambrian breakup of cratonic Au stralia. For these reasons, we suggest that the Lachlan Transverse Zone rep resents the reactivation of a fundamental crustal weakness in the cratonic lithosphere that propagated into younger Neoproterozoic to Palaeozoic litho sphere of oceanic and continental character.